While exploring the Subject Headings Linked Data Space (LCSH)
recently unveiled by the Library of Congress, I noticed that the
URI for the subject heading: World Wide Web, exposes an "owl:sameAs" link
to resource URI: "info:lc/authorities/sh95000541" -- in fact, a
URI.URN that isn't HTTP protocol scheme based.
The observations above triggered a discussion thread on Twitter that
involved: @edsu, @iand, and moi.
Naturally, it morphed into a live demonstration of: human vs
machine, interpretation of claims expressed in the RDF graph.
What makes this whole thing interesting?
It showcases (in Man vs Machine style) the issue of
unambiguously discerning the meaning of the owl:sameAs claim
expressed in the LCSH Linked Data Space.
Perspectives & Potential Confusion
From the Linked Data perspective, it may spook a few people to
see owl:sameAs values such as: "info:lc/authorities/sh95000541",
that cannot be de-referenced using HTTP.
It may confuse a few people or user agents that see URI
de-referencing as not necessarily HTTP specific, thereby attempting
to de-reference the URI.URN on the assumption that it's associated
with a "handle system", for instance.
It may even confuse RDFizer / RDFization middleware that use
owl:sameAs as a data
provider attribution mechanism via hint/nudge URI values derived
from original content / data URI.URLs that de-reference to nothing
e.g., an original resource URI.URL plus "#this" which produces URI.URN-URL
-- think of this pattern as "owl:shameAs" in a sense :-)
Unambiguously Discerning Meaning
Simply bring OWL reasoning (inference rules and reasoners) into
the mix, thereby negating human dialogue about interpretation which
ultimately unveils a mesh of orthogonal view points. Remember, OWL
is all about infrastructure that ultimately enables you to express
yourself clearly i.e., say what you mean, and mean what you
say.
Path to Clarity (using Virtuoso, its in-built Sponger Middleware,
and Inference Engine):
- GET the data into the Virtuoso Quad store -- what the sponger
does via its URIBurner Service (while following
designated predicates such as owl:sameAs in case they point to
other mesh-able data sources)
- Query the data in Quad Store with "owl:sameAs" inference rules
enabled
- Repeat the last step with the inference rules excluded.
Actual SPARQL Queries:
Observations:
The SPARQL queries against the Graph generated and
automatically populated by the Sponger reveal -- without human
intervention-- that: "info:lc/authorities/sh95000541", is just an
alternative name for < xmlns="http" id.loc.gov="id.loc.gov"
authorities="authorities" sh95000541="sh95000541"
concept="concept">, and that the graph produced by LCSH is
self-describing enough for an OWL reasoner to figure this all out
courtesy of the owl:sameAs property :-).
Hopefully, this post also provides a simple example of how
OWL facilitates "Reasonable Linked Data".
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